This invention relates to the shaping of bone. One technique of bone shaping is by resort to a saw, often an oscillating saw, but it will be understood that, in the broadest context, this invention relates not only to the sawing of bone, but also to various types of other abrading such as burr removal, reaming, grinding, cutting, milling, drilling, scraping, and even to electro-surgery and laser cutting devices.
Typically, such shaping equipment is used in orthopedics, and most often involves the use of saws to machine off portions of bone to fit prosthetics such as are used, for example only, in artificial knees and hips. Such shaping apparatus, often saws, are also used to cut pieces of bone out of hip sites, in order to form or shape a splice or fixation piece for operations on the spine, for example. Such pieces of bone must be extensively sawed and milled to shape.
In the course of such operations, the death or necrosis of bone tissue can be experienced any time the temperature resulting from shaping exceeds 130.degree. F. for any significant period of time. When such necrosis occurs, the tissue does not grow into the cut site, fracture site, or surface of the cementless prosthesis or other prosthesis and may fail to knit. In the absence of knitting, the prosthesis may not be anchored by bone growth, possibly resulting in the necessity to have a replacement operation some period of years thereafter, often called a "revision procedure." In some instances, half of all knee or hip operations may be revision procedures, often because in the initial operation, where temperature is a contributing factor, excessive temperatures were reached at the site of the shaped surface or bone kerf (or cut). Furthermore, in the absence of lubrication, small metal particles may be abraded from the saws and remain in the wound where they adversely affect long term viability of the tissue.
It has in the past beenerecognized that it would be desirable to cool the shaping devices during their operation, in order to keep heat build-up at a minimum. To such an end, it is known to apply fluid such as water to the tool by external means, such as by a syringe, in order to attempt to cool the tool at the shaping site.
U.S. Pat. No. 2,557,364 represents a prior art surgical saw blade.
U.S. Pat. Nos. 4,008,720 and 5,087,261 represent bone saws of the type in which an oscillating blade driver drives a bone saw in an oscillating motion, and in which means are provided for delivering a cooling liquid to the bone site. Such prior art devices either do not deliver cooling liquid directly to the cutting site, or provide limitations in the type of shaping member due to the manner of liquid delivery. In one known blade, nearly one third of the cutting tooth edge is removed to provide a conduit for the fluid.
It has also been found in connection with the shaping of bone, and particularly where a liquid is provided during such bone shaping for purposes of cooling the saw or other shaping member, that sprays or aerosols are generated. Such generation of sprays (or aerosols) at the site of the shaped bone (or kerf) create dangerous conditions, because of the dissemination of infections that might be present in the bone tissue, to the medical personnel attending the operation. For example, such infection might include hepatitis, AIDS, or the like. Prior art bone shaping apparatus and methods do not appear to have effectively addressed this serious concern.
To the extent that the prior art appears to have addressed the prevention of the dissemination of aerosols having the effluent of bone shaping, such as blood and tissue therein, such have generally proven to be inadequate. For example, mechanical barriers, such as transparent screens, may be provided, but visibility may be partially blocked as aerosols land on the screens, and such lack of visibility becomes detrimental to the operation. Consequently, in many cases, mechanical barriers are not utilized, and the medical personnel may often be observed with red, moist aerosol-caused accumulations of blood and tissue on their gowns, masks and caps, at the end of an operation.
U.S. Patent application Ser. No. 08/005,887, of which the present application is a continuation-in-part, and which is incorporated herein by reference, discloses a bone shaping device in which cooling liquid is provided through one or more conduits with openings located at the narrow sides of the shaping member. Application Ser. No. 08/005,887 also discloses an apparatus and method for containment of aerosols generated at the site of the bone shaping operation in which a gaseous fluid such as air impinges with the aerosols in order to drive the aerosols away from the shaping apparatus and toward the bone.